How insert a form data to mysql when checkbox is checked?

Welcome, I have some problem with form and insert data to mysql. My form have an input:

<inpu type="checkbox" name="check">

and this is my code to insert this form data to mysql.

if(isset($_POST['check'])) { //things to insert } 

and when i select one checkbox code inserting every record, when i select all checkboxes its also inserting a every record (all data). But when i not select a checkbox insert is empty (good). Whats wrong with this checkboxes?